Many industrial processes utilize emissions treatment systems to reduce the dissemination of various pollutants. Mercury, for example, is considered to be a toxic pollutant and its containment is heavily regulated. One of the most effective methods for removing pollutants such as mercury from industrial emissions is a treatment using activated carbon.
Activated carbon is a form of carbon processed to be riddled with small, low-volume pores that increase the surface area available for adsorption or chemical reactions. Powder activated carbon (PAC) is a particulate form of activated carbon, typically having fine granules less than 1.0 mm in size with an average diameter between 0.15 and 0.25 mm. PAC thus has a large surface to volume ratio with a small diffusion distance. In mercury treatment systems, PAC can adsorb vaporized mercury from flue gas and then be collected with fly ash in the treatment facility's particulate collection device, such as a bag house. However, PAC is somewhat hydrophilic and can compete for moisture with other compounds in an emissions treatment system.
For example, lime is used to remove acidic gases, particularly sulfur dioxide, from flue gases. In dry lime scrubbing treatments, lime is injected directly into flue gas to remove sulfur dioxide. A sulfur dioxide and lime contact zone, such as a spray dryer, provides space for mixing hot flue gas and lime slurry that is sprayed through an atomizer or nozzle. The lime slurry absorbs sulfur dioxide. The water in the lime slurry is then evaporated by the hot gas. A portion of the dried, unreacted lime and its reaction products fall to the bottom of the contact zone and are removed. The flue gas then flows to a particulate control device (e.g., the bag house) to remove the remainder of the lime and reaction products.
Because of PAC's moisture-competitive quality, emissions treatment systems utilizing both PAC and lime slurry may require significantly more lime slurry to adequately remove sulfur dioxide as compared to systems not using PAC. Accordingly, there exists a need to improve the efficient control and treatment of pollutants such as mercury and sulfur dioxide within a single system.